1. Field of the Invention
The present invention relates to a magnetic actuator and a haptic sense presenting device which enable reduced leakage of magnetic flux to the outside and can be operated in a stabilized manner.
2. Description of the Related Art
Recently, a magnetic actuator utilizing an electromagnetic interaction as a driving force has been widely used. For example, with the development of information transfer devices, a means for transmitting information through a haptic sense is needed in addition to a visual sense and an auditory sense, and a haptic sense presenting device incorporating a compact magnetic actuator into a pointing device such as a mouse or the like and capable of giving vibration to a fingertip has been realized.
A haptic sense presenting device incorporating a magnetic actuator has been disclosed in Japanese Patent Laid-Open Publication No. 2000-330688. As shown in FIG. 16A, a haptic sense presenting device is provided with a magnetic actuator in a pointing device 100, and a transmitting unit 18 is provided connected with the magnetic actuator. When in use, as shown in FIG. 16B, vibration from the magnetic actuator can be transmitted to a fingertip by keeping the fingertip in contact with the transmitting unit 18.
FIGS. 17 and 18 show a side view of the magnetic actuator incorporated in the haptic sense presenting device and an exploded perspective view of the major portion thereof, respectively.
The magnetic actuator comprises, as shown in FIG. 17, a magnet array 10, a plane coil 12, yoke plates 14a and 14b, a stud 16, a transmitting unit 18, a sliding unit 20, and a connecting unit 22. As shown in FIG. 18, the magnet array 10 comprises magnets 10a to 10d, and the plane coil 12 comprises plane coils 12a to 12d. 
The magnets 10a to 10d are juxtaposed on the yoke plate 14a with opposite polarity alternately directed. The plane coils 12a to 12d are kept away from the magnets 10a to 10d by a predetermined gap, respectively, and arranged so as to straddle a plurality of magnets, respectively. The yoke plate 14b is provided so as to cover the plane coil 12. Span between the yoke plate 14a and the yoke plate 14b is supported by the studs 16so as to keep a fixed interval.
The transmitting unit 18 is, as shown in FIG. 17, concurrently coupled with each of the plane coils 12a to 12d via the connecting unit 22. On the other hand, the transmitting unit 18 is also relatively slidably coupled to an outer member 26 by the sliding unit 20.
Between the yoke plate 14a and the yoke plate 14b, a magnetic field is generated by the magnets 10a to 10d. In the magnetic field, an electromagnetic force is generated for the plane coils 12a to 12d by applying an electric current to the plane coils 12a to 12d, thereby driving the transmitting unit 18. For example, as shown in FIG. 18, when north poles and south poles of the magnets 10a to 10d are arranged facing in the Z axis direction and the plane coil 12 is provided within the X-Y plane, a driving force can be generated within the X-Y plane.
The magnetic actuator incorporated in such a pointing device or the like is required to be as compact as possible, while its operable range is desired to be as large as possible. Moreover, in order to obtain the largest possible driving force for the size, it is necessary to prevent leakage of the magnetic flux to the outside and to increase the interaction between the magnetic field and a coil current. Furthermore, in order to avoid effects on outside equipment (for example, a display, a magnetic card, or the like), leakage of the magnetic field from the magnet in the magnetic actuator to the outside needs to be sufficiently suppressed.
However, the above-described conventional magnetic actuator has the following problems.
(A) In the upper and the lower parts of the magnetic actuator, the magnetic field leaked to the outside is restricted because the magnetic field is cut off by the yoke plates 14a and 14b. However, a yoke cannot be provided on the side of the magnetic actuator, because the members avoid interfering with one another when the plane coil 12 is moved, which means that leakage of the magnetic field from the side to the outside is larger than that from the upper and the lower parts thereof. Therefore, a magnetic field effective for generating a driving force is reduced and an effect on outside equipment is increased. Moreover, when the plane coil 12 moves further away from the center of the magnetic actuator, it is more susceptible to the influence of the reduction of the magnetic field due to the leakage of the magnetic flux from the side of the magnetic actuator, and a sufficient driving force cannot be obtained.
(B) When a yoke is provided on the whole area of the side of a magnetic actuator in order to avoid the above-described problem (A), the magnetic actuator itself must be made larger in order to obtain the operable range equal to the conventional one, thus a requirement for making it smaller in size and lighter in weight cannot be satisfied.
(C) In a magnetic actuator, when a plane coil 12 is moved to the vicinity of an end of a magnet 10, as shown in FIG. 19, one side of the plane coil 12 comes closer to the vicinity of the boundary of two magnets. In the vicinity of the boundary of the neighboring magnets, a north pole of the magnet is very close to a south pole of the magnet, and therefore a horizontal magnetic field directing from a north pole to a south pole is generated. The magnetic field causes a driving force in a direction straying away from the intrinsically required driving force toward the in-plane direction of the plane coil 12, as shown in FIG. 19.
Accordingly, when the plane coil 12 comes closer to the vicinity of the boundary of the magnets, a problem is caused that the plane coil 12 is tilted, or the plane coil 12 is further entangled with another member. Specifically, when the plane coil 12 is moved to the ends of the magnetic actuator in the X and the Y directions, a problem is caused that a driving force is generated substantially in the vertical direction for all the plane coils 12.